We are trying to sync a custom object related to Lead and contact. the sync with Custom Object related to contact worked well , but the sync with lead is showing up error ""The Object was modified In CRM since the sync was last enabled..." the process followed was as per the standard process (disable global sync> refresh schema> enable sync for custom object). not sure why this error is coming up.
Could find same issue being faced by other community users, Salesforce Custom Object Error Message , but not sure what the solution was, what i could understand from one of the user is its a conflicting object. but not sure how to identify the conflicting object and resolved this issue.
Have logged a support ticket. it would be great if someone here has any solution for this.
Indeed, you cannot have a custom object linking to both the lead and contact, from what I remember. we encountered a similar issue a while ago. Try to rename one of the relationships in Salesforce, so that Marketo sees them as different.